This invention relates to inductors for use in integrated circuitry, more particularly to inductor designs in which the coils are patterned during standard fabrication line processing and in which a magnetic core is deposited as a follow-on process.
Inductive components are critical to the design of many circuits. This is particularly true of many types of signal processing filters. This generally complicates the implementation of these designs as integrated circuits. While available to GaAs designers, inductors have rarely been used in silicon designs. In GaAs technology, the frequencies involved for analog designs using physical inductors are typically on the order of 10.sup.10 Hz. CMOS transistors will not function at these high frequencies. It is of great interest that designs in CMOS operate in the 10.sup.5 -10.sup.8 Hz range. Hence, CMOS inductors must be on the order of 10.sup.2 -10.sup.5 times larger than those used in GaAs. This implies the necessity of inductors in the range of 0.001-1.0 mH.
In silicon integrated circuit microchips which require inductive components, designers usually resort to simulating a passive inductance using an active filter configuration comprising capacitors and resistors, or else attach the inductive components external to the chip. Both approaches work against the miniaturization of the circuit, and severely limit performance and applications.
Some integrated inductors have been proposed, but they generally require exotic materials and new fabrication processes. For example, in U.S. Pat. No. 3,614,554, a thinfilm inductor design is disclosed in which an inductor coil with a magnetic core is formed in layers, the coil axis and core being parallel to the layers. This patterning of a magnetic core prevents the coils from being fabricated using standard CMOS processes.